ABSTRACT Project 1 (Wondrak, Dickinson) TLR4 as a Novel Target for Skin Cancer Prevention Nonmelanoma skin cancer (NMSC) is the most common malignancy worldwide and is rapidly increasing in incidence, representing an expanding public health and economic burden. Cutaneous exposure to solar ultraviolet (UV) radiation is a major causative factor in skin carcinogenesis, and improved molecular strategies for efficacious chemoprevention of NMSC are urgently needed. Inflammatory signaling through TLR4 (Toll-like receptor 4) has been shown to drive skin inflammatory dysregulation and chemical carcinogenesis. Our own data demonstrate for the first time that pharmacological TLR4 antagonism can suppress UV-induced stress signaling and photocarcinogenesis in cultured keratinocytes and SKH-1 mouse models. Using TLR4-directed genetic and pharmacological experimentation, we propose to test the novel hypothesis that this receptor is a major mediator and therapeutic target in skin photocarcinogenesis. To this end, we will first use transgenic mouse models to examine the role of keratinocyte-derived TLR4 signaling as a crucial mediator of acute UV- induced photodamage, photoimmunosuppression and photocarcinogenesis. These models will compare the responses of wildtype mice to those of epidermis-specific TLR4 knockout mice as well as total TLR4 knockout mice on the SKH-1 hairless background (Aim 1). Next, the feasibility of pharmacological modulation of TLR4 signaling for skin cancer photochemoprevention will be tested in acute and chronic UV-exposed mouse models (Aim 2). Our recent preliminary findings show that our lead compound, resatorvid (TAK-242, a specific covalent TLR4 small molecule inhibitor) significantly inhibits UV-induced tumorigenesis in SKH-1 mice. Thus, the acute and chronic studies of Aim 2 are focused upon comparing resatorvid to other lead TLR4 pathway inhibitors, as well as upon testing the efficacy of a clinically-relevant cream formulation of one of the lead compounds (developed by Core D) on mice in the interest of aiding forthcoming clinical trials performed by Project 3. Finally, as a developmental aim, we will compare the effects of clinically-relevant TLR4 agonists and antagonists on UV-induced apoptosis and stress signaling in both cell culture and SKH-1 mouse skin. The preclinical and translational results of these studies will inform our ability to therapeutically target the TLR4 pathway as a means of preventing NMSC in responsive populations.